Sheet stacker and control stack removing means

ABSTRACT

A sheet conveyor is provided for depositing sheets onto a stack with the conveyor discharging end being moved progressively upward as the stack height increases with a stop plate being positioned forward of the discharge end of the conveyor and mounted on adjustable horizontally movable arms for adjustment to the size of the sheet being stacked with the sheets being deposited on a reversible power driven conveyor and safety contact switch means being provided on the sheet conveyor and with control switch means on the discharge side of the stop plate for enabling a close spacing of successively formed sheet stacks.

United States Patent Lucas 154] SHEET STACKER AND CONTROL STACK REMOVINGMEANS [72] inventor: Raymond L. R. Lucas, Avenue de la Republique,Prechac, France [22] Filed: Nov. 30, 1970 [21] App1.No.: 93,747

[30] Foreign Application Priority Data Dec. 22, 1969 France ..6944504[52 us. Cl. ..27l/68, 2 14/6 0 [51] Int. Cl. ..B65h 29/50 [58] Field ofSearch ..27l/68, 86; 214/6 G [56] References Cited UNITED STATES PATENTS3,321,202 5/1967 Martin ..27l/68 1,389,244 8/1921 Free ..27l/68 [451Oct. 17,1972

3,549,144 12/1970 Lucas ..271/68 Primary Examiner-Evon C. BlunkAssistant Examiner-Bruce H. Stoner, Jr.

Attorney-Mason, Fenwick & Lawrence [5 7] ABSTRACT A sheet conveyor isprovided for depositing sheets onto a stack with the conveyordischarging end being moved progressively upward as the stack heightincreases with a stop plate being positioned forward of the dischargeend of the conveyor and mounted on adjustable horizontally movable armsfor adjustment to the size of the sheet being stacked with the sheetsbeing deposited on a reversible power driven conveyor and safety contactswitch means being provided on the sheet conveyor and with controlswitch means on the discharge side of the stop plate for enabling aclose spacing of successively formed sheet stacks.

6 Claims, 8 Drawing Figures PATENTED 17W? 3,698,707

sum 1 BF 3 INVENTOR QAYMQND L-E. Lucas ATTORNEYS PATENTEUBN 1 13.698.707

SHEU 2 BF 3 ilg-a- RAYMOND R. Lucas Mus im f ATTORNEYS SHEET STACKER ANDCONTROL STACK REMOVING MEANS The subject invention is in the field ofstacking machines and is specifically directed to improvements in stopor gauge plates employed for forming vertical stacks of planar memberssuch as sheets formed of corrugated cardboard, fiberboard or the like.Specifically, the invention is directed to a new and improved adjustableguide and support means for a stop plate situated in front of thedischarge end of a sheet feeding conveyor belt head. The stop orabutment plate is held in a vertical position by two horizontal armswhich are horizontally adjustable in accordance with the size of thesheets to be stacked. These horizontal arms slide in supports pivotableabout the axis of the stacker head of the conveyor and are held inparallel horizontal arrangement by a parallelogram linkage of which oneside of which is the frame of the machine.

Prior experience has shown that previously known stop devices of thetype rigidly attached to horizontal arms sliding in and extending fromthe conveyor frame element which supports the sheet conveyor belt aredifficult to operate and frequently provide a source of danger to theoperator who must, during the formation of a stack, occasionally reachto the center of the stack in order to straighten out the pile or toremove small particles of trash, clippings, chips or the like.

Additionally, the prior known rigid systems employ horizontal arms and avertical abutment or stop plate fixed at the end of the arms isfrequently subject to malfunction or damage since a descending movementof the stop plate from an upper position to a lower position can causethe plate to engage misplaced stacks or other items and consequentlyinflict damage upon the engaged items or to the stacker assembly itself.This fact has resulted in inconvenience and inefficiency of operationdue to a variety of other factors such as the desirability of providingcompleted piles travelling in fixed relationship on an outfeed conveyorrather than in irregular relationship. Consequently, efficiencyfrequently suffers due to the substantial time required for removingsuccessive stacks from the stacker.

The instant invention constitutes a modification of the prior knownsystems and enables the obtainment of considerable advantage thereoverboth in technical ease of operation and economy of operation, not tomention the provision of greater safety for the operator of the machine.

Specifically, the subject invention employs a pair of horizontallaterally spaced cantilever arms for supporting the vertical stop platewith the horizontal arms being positioned very near the longitudinalaxis of the stacking conveyor in a slide bearing type support providedwith means for guiding the arms and for adjustably positioning the armsin relation to the sheets being stacked.

It should be noted that the previously known arrangement of support armsand stopplates have been in the form of an integral construction withthe plate extending integrally or in a fixed manner from the end of thearms. The present invention, on the other hand, provides support for thestop plate in a slide bearing system arranged at the end of the armswith the plate being normally held at the lower end of the slide byvirtue of the force of gravity but being movable upward if an upwardforce should be applied to it. During the return movement of the stackerhead from its upper position to its lower position following thecompletion of a stack, any obstacle which is engaged by the lower edgeof the stop plate is not damaged since the stop plate merely movesupwardly within the slide in which it is retained. Such upward movementof the plate with respect to its supporting slide bearing serves toactuate an electric switch connected to the control for the motoremployed in lowering the discharge end of the conveyor for deactivatingthe motor. The operator can then remove the object with which the stopplate is engaged in order to reactivate the motor and continue downwardmovement of the discharge end of the conveyor. Consequently, the instantinvention provides a safety feature which avoids damage to articlespositioned beneath the descending stop plate and also serves to avoidunfortunate injuries to the operator of the device.

Additionally, the subject invention provides means whereby the adjacentstacks deposited on a stack receiving and removing belt areautomatically removed in response to the sheet conveyors reaching itsupper limit of travel upon completion of each stack. This dischargemovement of the completed stack is calculated to produce a suitablearrangement and spacing of the successive stacks on the belt and alsopermits a free descent of the stacker head following the completion ofthe stack in order to initiate the formation of the next stack. Arrivalof the discharge end of the stacker conveyor at its lowermost positionserves to activate an electrical switch which initiates operation of thestack receiving and removing belt in a reverse direction to return thejust completed stack against the outer face of the stop plate. The stopplate is, in turn, equipped with an electric switch on its outer facewhich stops the return movement of the stack receiving and removingbelt. Consequently, the next stack to be formed will be separated fromthe last formed stack solely by the thickness of the stop plate.

Another feature of the present invention is that the horizontal stopplate support arms form a unique undeformable mechanical unitindependent of the stop plate. The unit consists of the horizontal armswhich are positioned closely together and which are joined at one end bya slide which provides support for the stop plate and at its other endby a cross piece. The axis of this mechanical system is situated in thelongitudinal plane of the stacker conveyor. Consequently, lateraltwisting forces from the arms to the sheet conveyor will be minimized.

Another significant feature of the present invention is the employmentof a casing type support at the center of a crosspiece that links thetwo horizontal supports for the stop plate. A number of rollers some ofwhich are mounted for rotation about a vertical axis and the other ofwhich are mounted for rotation about a horizontal axis provide supportfor the horizontal arms. The mechanical system for supporting thehorizontal arms supporting the stop plate enables reciprocal adjustmentin a horizontal plane of the arms by virtue of the arms being supportedby the rollers. Consequently, the support system provides an easilyadjustable positioning of the stop plate a given distance away from thedischarge end of the sheet conveyor for enabling the stacking of varioussize sheets.

A better understanding of the subject invention will be enabled by thefollowing description with reference to the drawings in which:

FIG. 1 is a side elevational view of the preferred embodiment of theinvention;

FIG. 2 is a plan view of the preferred embodiment with some parts notillustrated for the sake of clarity;

FIG. 3-A is a side elevational view illustrating a stack being formed onthe receiving and removing conveyor;

FIG. 3B is a side elevational view similar to FIG. 3-A illustrating acompleted stack prior to removal of the stack from the stacking station;

FIG. 3-C is a side elevational view illustrating the position of thecompleted stack following initial removal of the stack from the stackingposition;

FIG. 3-D is a side elevational view illustrating return movement of thecompleted stack to a position adjacent the outside of the stop plate;

FIG. 3-E is a side elevational view illustrating the formation of asecond stack which is being formed adjacent the first stack; and

FIG. 4 is a schematic diagram of electrical circuitry usable forcontrolling the stacking components.

A sheet feeding stacking conveyor supported by two (only one of which isshown in FIG. 1) conveyor supporting side frame members I is providedwith a head roller 2 which supports an endless sheet feed discharge belt3, the upper flight of which is moving to the left in FIG. 1 and whichfeeds sheets to be stacked to a stacking or depositing station generallydesignated D. A guide support frame 4 is positioned on each side of theconveyor frame elements 1 (only one of the guide support frame elements4 is illustrated in FIG. 1). Each of the guide support frame members 4is pivotally connected for pivotal movement about the axis of roller 2and is maintained in a vertical orientation by virtue of a rocking lever5 connected to the frame 4 on one end and connected on its other end tothe main machine frame F of the stacker (FIG. 3-A). There isparallelogram relationship between the elements 5, 4, 1 and the mainframe F to which elements 1 and 5 are pivotally connected so that theguide support frames 4 are maintained in vertical orientation at alltimes.

A tubular crosspiece 6 is fixedly attached to the upper ends of thesupport frames 4 and extends laterally in relation to the conveyor belt3 as is clearly shown in FIG. 2 of the drawings. First and secondvertical side plates 7 and 7-A are welded to the transversely extendingsupport member 6. A pair of horizontal plates 8 and 9 (FIGS. 1 and 2)are connected to the side plates 7 and 7-A and horizontal arms 10 and10-A (FIG. 2) are mounted for axial horizontal movement between theplates 8 and 9 by means of horizontal axis rollers 18 and vertical axisrollers 19 respectively supported on plates 7, 7-A and 9.

Additionally, the horizontal arms 10 and l0-A are connected to eachother by means of a crosspiece 11 adjacent their rearmost ends (theright as viewed in the drawings) and are connected on their other endsto a vertically oriented slide bar 12. Slide bar 12 is supported by sideplates 13 and 13-A which are attached to the side of the horizontal arms10 and 10-A as best shown in FIG. 2. Each of the side plates 13 and 13-Acarries a set of four rollers 14 which are mounted for rotation onhorizontal arms perpendicular to the axes ofarms l0 and 10-A.

A stop or gauge plate 15 is mounted for vertical movement by virtue of apair of U-shaped channel members 17 and 17-A which are attached toextend from the deposit station facing side of plate 15 toward the rightas viewed in FIG. 2 and have a rearmost flange receivable within therespective rollers 14 on each side of the horizontal arms 10 and 10-A.Consequently, the U-shaped channel members 17 and 17-A are capable ofcontrolled vertical movement along with their attached gauge or stopplate 15. Additionally, the stop plate 15 is provided with ahorizontally extending rigid base member 16 extending across its entirewidth which provides reinforcement for the plate.

A horizontal guide and locking rod 20 extends parallel to the horizontalarms 10 and 10-A between the crosspiece 11 and the vertical slide bar 12and supports a split ring type clamp member 21 which can be adjustablypositioned at any point along the length of the rod 20 and which can beclamped thereto in an obvious manner. The adjustment of the rod 20 withrespect to the horizontal plate 8, etc., serves to position the stopplate 15 at a desired horizontal distance in front of the discharge endof conveyor 3 in accordance with the size of sheets to be dischargedfrom the conveyor 3. It should be noted that the rod 20 is fixedlyattached to both the crosspiece 11 and the vertical slide bar 12. Alever 21' is operably mounted on split ring clamp 21 for enablingloosening of the clamping action of the clamp to rod 20 to permitadjustment of the position of clamp 20 on the rod and subsequenttightening of the clamping member to retain same in a desired adjustedposition on the rod 20.

An electric switch 22 is connected to the upper portion of the verticalslide bar 12 (FIG. 1) for permitting operation of the stackingmechanism. A horizontally extending switch actuating flange 17-B extendsover switch member 22 and normally rests on a switch actuating plungeror arm of the switch for closing the contacts of the switch. However,since flange 17-8 is connected to the channel members 17 and 17-A, alongwith the stop plate 15, vertical upward movement of the stop plate 15with respect to switch 22 serves to permit the contacts of switch 22 toopen. A second electric switch 23 is mounted with its actuator arm 23'on the outer or downstream face of the stop plate 15 for controlling themovement of a completed pile of sheets in a manner to be discussed in'detail hereinafter. Switch 23 is for interrupting electric current to adrive motor 60 of a stack receiving and removing conveyor 30 whichconveys the completed stacks away from the stacking station. The drivemotor 60 of conveyor 30 is reversible for a purpose stated hereinafterand during a reverse operation the engagement of a completed stack withthe switch arm 23 serves to open switch 23 to deactivate the motor todiscontinue reverse movement of the stack to the right.

Additionally, an electric switch 24 attached to plate 8 is provided forinitiating the operation of the stacker for the formation of a newstack. Switch 24 is controlled by a switch actuator plate 25 extendingfrom the adjustable stop clamp member 21 mounted on rod 20. Anadjustable spring bias stop member 26 carried by plate 8 is positionedon the side of plate 25 opposite switch 24 as shown in FIG. 2 to limitmovement of plate 8 with respect to actuator plate 25.

Additionally, pressure responsive switch actuator elements 27, 28 and 29are provided for deactivating the motor (not shown) for driving theconveyor frames 1 downwardly during descent of the conveyor frame in theevent that any of these switch actuator elements engages in immovableobject such as the operators hand, a misplaced stack or other improperlypositioned member.

It should be understood that actuator elements 27, 28 and 29 can beconventional pressure responsive planar pad type switch members or canbe switch actuator lever arms if such should be desired. Planar typeswitch actuators of the type contemplated are frequently employed forautomatically opening doors or the like in response to the pressure of aperson approaching such electrically controlled doors.

It can be seen that the adjustment of the stop member 21 and itsassociated finger lug 25 on bar 20 is determined in accordance with thesize of the sheets to be stacked and the closing of the switch 24 servesto actuate the motor for providing pivotal movement of .frame 1 toinitiate a slow upward movement of the discharge end of the conveyor(the end with roller 2, etc.) The conveyor is operated until the stackhas reached a predetermined height. Following completion of a stack,lifting movement of the discharge head of the conveyor continuesalthough no additional sheets are being fed by the conveyor 3 until theabutment or stop plate completely clears the completed stack so that thestack can be removed to the left by conveyor Electrical voltage issupplied by main conductors 38, 40 and the parts are in the positionshown in FIG. 3-A as a stack S1 is being formed as sheets are fedinwardly by the conveyor 3 against the stop plate 15 and deposited onthe stack S1 supported on a pallet 69 on conveyor 30. The control anddrive means for moving the discharge end of conveyor 3 gradually upwardis preferably of the type shown in my copending application Ser. No.743,419 U.S. Pat. No. 3,549,144, and continues to be operated followingcompletion of the stack and is lifted above the top of stack S1 asillustrated in FIG. 3-B.

Following termination of the upward movement of plate 15, switch meansCB2 of relay CB is closed by operation of timer T or manually for apredetermined period of time to operate the drive motor 60 for drivingthe stack receiving and removing conveyor to the left in the directionof the arrow shown in FIG. 3-C. Following termination of movement of thecompleted stack S1 to the left to the approximate position illustratedin FIG 3-C, a down relay R2 is actuated either manually or by timingcontrol circuit T for initiating lowering movement of the discharge endof the conveyor 3 to lower the conveyor and the stop plate 15 to theposition shown in FIG. 3-C.

Since stack S! has been moved to the left from the vicinity of the stopplate 15, there is no impediment to the lowering of stop plate 15.However, if the switches 28, 29, etc., should engage an obstacle duringthe descent of the conveyor 3, the down relay R2 controlling theconveyor tilt motor (not shown) for effecting downward movement of thedischarge end of conveyor 3 will be immediately deactivated to terminatesuch movement. Similarly, upon arrival of the discharge end of conveyor3 at its lowermost position, the plate 15 engages the conveyor 30 and ismoved upwardly to open switch 22 to terminate actuation of the downrelay R2.

Following the arrival of the discharge end of the conveyor 3 in itslowermost stack initiating position shown in FIG. 3-C, a switch 61 isclosed by timer T or manually for actuating a reverse drive conveyorrelay CC to close contacts CC2 for an adequate period of time to operatemotor in a reverse direction to cause the conveyor 30 to move to theright as shown in FIG. 3-D so that the completed stack S1 is movedrightwardly until it abuts against the left side of the stop plate 15.Engagement of stack S1 with the stop plate 15 immediately opens switch23 to deactivate the reverse drive relay CC and consequently terminatesreverse drive of conveyor 30 by motor 60. Moreover, engagement of thestack 51 with the plate 15 also serves to shift the plate 15 to theright sufficiently to close contacts 24 which consequently initiatesanother cycle of operation of the timer control circuit T. It should beunderstood that the various switches 52, 54, 50, 61, etc., can bemanually operated or automatically operated by controlled timer switchunits in the schematically illustrated timer circuit T. Moreover, bothmanual and automatic operation can be provided in a manner obvious tothose skilled in the art.

Following closure of switch 24, the feeding of sheets onto conveyor 3 isinitiated by timer T along with the required closure of contacts 52 tostart the upward movement of the discharge end of conveyor 3 byactivation of an up relay R1 which makes the motor controlling thedischarge head of the conveyor move the head upwardly as a second stackis being built. Consequently, a new stack S2 is begun as shown in FIG.3-15 and the sheets continue to be fed until the stack S2 is completed.Following completion of stack S2, the discharge end of conveyor 3continues to move upwardly in a previously discussed manner so that thelower edge of the plate 15 will be above the top of stack S2 at whichtime relay R1 is deactivated to stop upward movement of the conveyor 3.The stack receiving conveyor 30 is then activated to remove the stack tothe left in the same manner as stack 81 was moved. The discharge end ofthe conveyor is again lowered following actuation of relay R2 and stackS2 is moved to the right to open switch contact 23 and close contacts 24to initiate another cycle of operation.

Consequently, it will be seen that the subject inventive arrangementenables an optimum close spacing of the successively completed stacks onconveyor 30.

If, during the descent of the stacker head, an obstacle should engagethe lower edge of the abutment or stop plate 15, the plate is pushedupwardly by virtue of its sliding movement enabled between the rollers14 and electrical switch 22 is opened to deactivate relay R2 toconsequently automatically break the power circuit to the motor forlifting and lowering the discharge head of conveyor 3 to consequentlystop the descending movement of the discharge head.

I claim:

1. In a sheet stacker of the type having a pivotally mounted sheetconveyor belt with a discharge head for discharging sheets onto a stackreceiving and removing conveyor and means for moving the conveyordischarge head in an arcuate path from a lowermost position to anuppermost position as the height of the stack being formed increases,the improvement comprising a vertical stop plate, two horizontalparallel arm members joined on each end to form a unitary constructionmounted for axial movement in slide means attached to the dischargehead, adjustable means for axially adjusting the position of saidhorizontal arms with respect to said discharge head for supporting saidstop plate in adjustable positions in spaced horizontal relationship tothe discharge head, said arm means extending adjacent the verticallongitudinal plane of the sheet conveyor in a horizontal plane and guidemeans comprising a series of rollers mounted adjacent the ends of saidarms opposite said discharge conveyor supporting said stop plate bymeans of a U-shaped channel member connected to the stop plate andextending between the series of rollers for permitting limited movementof said stop plate relative to said horizontal arm means perpendicularto said horizontal arm means.

2. The invention of claim 1 additionally including safety switch meansupon which means supporting said stop plate rests when said stop plateis in its lowermost position whereby vertical movement of said stopplate with respect to said switch means as would occur upon theengagement of the lower edge of said stop plate with an obstacle duringlowering movement of the discharge head of said conveyor serves todeactivate saidsafety switch to stop the lowering movement of saiddischarge head.

3. The invention of claim 2 additionally including a stack sidedetecting switch means mounted on said stop plate for detecting a stackmoved against the side of said abutment plate opposite said dischargehead and a second switch mounted on means fixed to said horizontal armsfor actuation upon bodily movement of said stop plate towards saiddischarge head for activating said conveyor pivoting motor to initiate asubsequent stacking cycle.

4. In a sheet stacker of the type having a pivotally mounted sheetconveyor belt with a discharge head for discharging sheets onto a stackreceiving and removing conveyor driven by selectively operablereversible drive means, and means for moving the conveyor discharge headin an arcuate path from a lowermost position to an uppermost position asthe height of the stack being formed increases, the improvementcomprising two horizontal, parallel arm members connected to thedischarge head of the conveyor, extending outwardly over said stackreceiving and removing conveyor, guide means mounted on the outer endsof said arm members, said guide means supporting a stop plate normallymaintained in a lower position on said guide means by gravity, butmovable to an upper position with respect to said guide means and armmembers, switch means positioned adjacent said stop plate actuated bymovement of said stop plate to said upper position for terminatingdownward movement of said discharge head upon engagement of said stopmeans with any fixed object or with said stack receiving and removingconveyor means.

5. The invention of claim 4 wherein said arm means is supported on saiddischarge head for limited axial movement between a forward extendedposition and a retracted osition in which said stop plate is positionedclosely a acent said discharge hea biassmg means for urging said stopplate and said arm means toward said extended position and switch meansengageable with means connected to said arm means for actuation uponmovement of said arm means and stop plate to said retracted positioncaused by engagement of a completed stack with the outer surface of saidstop plate when said stack receiving and removing conveyor moves a stackagainst said outer surface of said stop plate for initiating a newstacking cycle in which a second stack will be provided adjacent saidfirst stack but spaced therefrom by the width of said stop plate.

6. A method of stacking sheets with a stacker of the type having apivotally mounted sheet conveyor belt with a discharge head fordischarging sheets at a stacking station against a stop plate mounted onthe discharge head onto a stack receiving and removing conveyor drivenby reversible drive means, said method comprising the steps of:

forming a first stack as said discharge head moves upwardly whilecontinuously feeding sheets forming said stack;

discontinuing the feed of sheets from said discharge head when saidfirst stack reaches a desired height while said discharge head continuesto move upwardly;

discontinuing upward movement of the discharge head when the lowermostportion of the stop plate rises above the top of the first stack;

actuating said stack receiving conveyor in a forward direction to removethe first stack from the

1. In a sheet stacker of the type having a pivotally mounted sheetconveyor belt with a discharge head for discharging sheets onto a stackreceiving and removing conveyor and means for moving the conveyordischarge head in an arcuate path from a lowermost position to anuppermost position as the height of the stack being formed increases,the improvement comprising a vertical stop plate, two horizontalparallel arm members joined on each end to form a unitary constructionmounted for axial movement in slide means attached to the dischargehead, adjustable means for axially adjusting the position of saidhorizontal arms with respect to said discharge head for supporting saidstop plate in adjustable positions in spaced horizontal relationship tothe discharge head, said arm means extending adjacent the verticallongitudinal plane of the sheet conveyor in a horizontal plane and guidemeans comprising a series of rollers mounted adjacent the ends of saidarms opposite said discharge conveyor supporting said stop plate bymeans of a U-shaped channel member connected to the stop plate andextending between the series of rollers for permitting limited movementof said stop plate relative to said horizontal arm means perpendicularto said horizontal arm means.
 2. The invention of claim 1 additionallyincluding safety switch means upon which means supporting said stopplate rests when said stop plate is in its lowermost position wherebyvertical movement of said stop plate with respect to said switch meansas would occur upon the engagement of the lower edge of said stop platewith an obstacle during lowering movement of the discharge head of saidconveyor serves to deactivate said safety switch to stop the loweringmovement of said discharge head.
 3. The invention of claim 2additionally including a stack side detecting switch means mounted onsaid stop plate for detecting a stack moved against the side of saidabutment plate opposite said discharge head and a second switch mountedon means fixed to said horizontal arms for actuation upon bodilymovement of said stop plate towards said discharge head for activatingsaid conveyor pivoting motor to initiate a subsequent stacking cycle. 4.In a sheet stacker of the type having a pivotally mounted sheet conveyorbelt with a discharge head for discharging sheets onto a stack receivingand removing conveyor driven by selectively operable reversible drivemeans, and means for moving the conveyor discharge head in an arcuatepath from a lowermost position to an uppermost position as the height ofthe stack being formed increases, the improvement comprising twohorizontal, parallel arm members connected to the discharge head of theconveyor, extending outwardly over said stack receiving and removingconveyor, guide means mounted on the outer ends of said arm members,said guide means supporting a stop plate normally maintained in a lowerposition on said guide means by gravity, but movable to an upperposition with respect to said guide means and arm members, switch meanspositioned adjacent said stop plate actuated by movement of said stopplate to said upper position for terminating downward movement of saiddischarge head upon engagement of said stop means with any fixed objector with said stack receiving and removing conveyor means.
 5. Theinvention of claim 4 wherein said arm means is supported on saiddischarge head for limited axial movement between a forward extendedposition and a retracted position in which said stop plate is positionedclosely adjacent said discharge head, biassing means for urging saidstop plate and said arm means toward said extended position and switchmeans engageable with means connected to said arm means for actuationupon movement of said arm means and stop plate to said retractedposition caused by engagement of a completed stack with the outersurface of said stop plate when said stack receiving and removingconveyor moves a stack against said outer surface of said stop plate forinitiating a new stacking cycle in which a second stack will be providedadjacent said first stack but spaced therefrom by the width of said stopplate.
 6. A method of stacking sheets with a stacker of the type havinga pivotally mounted sheet conveyor belt with a discharge head fordischarging sheets at a stacking station against a stop plate mounted onthe discharge head onto a stack receiving and removing conveyor drivenby reversible drive means, said method comprising the steps of: forminga first stack as said discharge head moves upwardly while continuouslyfeeding sheets forming said stack; discontinuing the feed of sheets fromsaid discharge head when said first stack reaches a desired height whilesaid discharge head continues to move upwardly; discontinuing upwardmovement of the discharge head when the lowermost portion of the stopplate rises above the top of the first stack; actuating said stackreceiving conveyor in a forward direction to remove the first stack fromthe stacking station; lowering the discharge head to position the stopplate adjacent the stack receiving conveyor; operating said stackreceiving conveyor in a reverse direction to return the first stack to aposition adjacent the stacking station engaging the downstream side ofthe stop plate and initiating the formation of a second stack in thesame manner as the first stack whereby the first and second stacks willbe closely spaced a distance only slightly greater than the thickness ofthe stop plate.